With the consent of Drs. Emre Kokman, Vijay Chandra, and Bruce Schoenberg (co-investigators), all incident cases of Alzheimer's Disease (AD) identified between 1965 and 1974 were made available to the Principal Investigator for three studies on this sample of 268 cases of clinically diagnosed AD. All medical records as well as state hospital records and nursing home records will be reviewed in order to identify psychiatric symptoms and psychiatric disorders which occurred in these patients throughout their lifespan. These symptoms and disorders will be divided into those occurring pre- and post- the onset on AD. A second study which will require review of all hospitalizations to identify all episodes of deliria (nocturnal disorientation) which occurred, will classify these episodes as pre- or post- the onset of AD. A third study will require the identification of all patients with clinically diagnosed AD and a major depressive episode (MDE). These will serve as the cases in a case-control study assessing MDE as a precursor or predisposing factor for AD. The two sets of controls will be identified from 1) age, sex, and race-matched controls with AD and no prior history of a MDE and 2) "normal controls" defined as matched for age, sex, and race, who do not have AD.